Apparatus and method for controlling the introduction of chemical foamant into a water stream in fire-fighting equipment
First Claim
1. In a fire system of the type including a water supply means for normally delivering water at varying flow rates through a hose member, means for monitoring the flow of water through said hose member and producing an electrical signal related to the rate of water flow through said hose member, a supply tank for containing a supply of a liquid chemical foamant, positive displacement pump means having an input port coupled to said supply tank, an output port coupled to said hose member and pump speed sensing means for sensing the speed at which said pump is being driven, a variable speed electrical motor for driving said pump means at a speed determined by a control signal applied thereto, computing means coupled to receive said electrical signal relating to flow and a signal from said pump speed sensing means, said computing means determining the speed at which said motor should be driven to introduce a metered quantity of said chemical foamant into said hose member, depending on the rate of flow of water through said hose member, the improvement comprising:
- (a) motor drive means coupled to said computing means for generating said control signal for said drive motor, said motor drive means producing a pulse width modulated signal of a predetermined frequency whose duty cycle is determined by said computing means for varying the speed of said drive motor between a maximum and a lower intermediate speed; and
(b) burst width modulating means for turning said pulse width modulated signal on and off at predetermined time intervals determined by said computing means for varying the speed of said drive motor between said lower intermediate speed and a predetermined minimum speed whereby the flow rate of said liquid concentrate into said hose member is controllable over an extended range.
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Accused Products
Abstract
A fire-fighting system in which a liquid chemical foamant is introduced into the water stream in varying amounts so as to maintain a predetermined percentage mixture irrespective of variations in the water flow includes a motor-driven pump where the motor is controlled over a first speed range by pulse width modulating the drive to the motor and over a second speed range, producing intermittent motion, by burst width modulating the drive signal when it is operating at its minimum pulse width modulated duty cycle. Using this technique the range of available motor speeds is extended well beyond that which can be achieved using pulse width modulation of the motor drive signal alone.
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Citations
10 Claims
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1. In a fire system of the type including a water supply means for normally delivering water at varying flow rates through a hose member, means for monitoring the flow of water through said hose member and producing an electrical signal related to the rate of water flow through said hose member, a supply tank for containing a supply of a liquid chemical foamant, positive displacement pump means having an input port coupled to said supply tank, an output port coupled to said hose member and pump speed sensing means for sensing the speed at which said pump is being driven, a variable speed electrical motor for driving said pump means at a speed determined by a control signal applied thereto, computing means coupled to receive said electrical signal relating to flow and a signal from said pump speed sensing means, said computing means determining the speed at which said motor should be driven to introduce a metered quantity of said chemical foamant into said hose member, depending on the rate of flow of water through said hose member, the improvement comprising:
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(a) motor drive means coupled to said computing means for generating said control signal for said drive motor, said motor drive means producing a pulse width modulated signal of a predetermined frequency whose duty cycle is determined by said computing means for varying the speed of said drive motor between a maximum and a lower intermediate speed; and (b) burst width modulating means for turning said pulse width modulated signal on and off at predetermined time intervals determined by said computing means for varying the speed of said drive motor between said lower intermediate speed and a predetermined minimum speed whereby the flow rate of said liquid concentrate into said hose member is controllable over an extended range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification